5i'
SECTION 6
TESTING AND MAINTENANCE
Recommendation Q.490
TESTING AND MAINTENANCE
6.1 General
In international working the guiding principles and testing
arrangements for maintenance as defined in Recommendations M.700
to M.728 and Q.134 also apply to Signalling System R2. The organi-
zation of routine maintenance, tests and measurements of signalling
and switching should comply with Recommendations M.716, M.718,
M.719, M.728 and M.732.
The analogue line signalling of System R2 differs from other
CCITT signalling systems in two significant respects:
- line signals are sent over out-band signalling
channels;
- an "interruption control" protects the line sig-
nalling from the consequences of interruptions of the transmission
path.
These two features of System R2 require special attention from
a maintenance point of view.
6.2 Automatic procedures for transmission measurements and
signalling tests
Circuits operated with System R2 require elaborate transmis-
sion measurements and signalling tests and also rapid and simple
testing of transmission and signalling. Both needs are preferably
met by means of automatic devices.
The specification for ATME-2 as adopted by CCITT makes it
applicable to the testing of international circuits using
System R2. The necessary information for its use on such circuits
is contained in Recommendation O.22.
A description of a simplified programme for rapid testing of
signalling and checking the transmission quality of a circuit is
given in S 6.3. Generally speaking, the arrangements for automatic
testing consist of outgoing test equipment connected at the outgo-
ing end of the circuit and incoming test equipment connected at the
incoming end.
6.3 Automatic test procedures for test equipments
Automatic test procedures provides a means for rapid testing
of signalling and also checking the transmission quality of cir-
cuits operated with Signalling System R2.
6.3.1 Numbering of access to test equipment
In international working, to set up a call to maintenance
equipment via circuits operated with System R2, the following mul-
tifrequency signals must be sent:
- I-13 (replacing the language digit, in accordance
with Recommendation Q.133),
- I-13,
- two digits "XY" which will be associated with the
type of test equipment and the procedure for testing to be employed
(see Recommendation Q.107, Table 7),
- I-15 (if requested by the incoming equipment).
Provision is made for repetition of signal I-13 to avoid com-
plications in the incoming R2 register in the country of destina-
tion. The second signal I-13 is stored in the place where the first
digit of the routing information is normally recorded. In this way,
access to the test equipment requires no analysis, for routing pur-
pose, of the signal which takes the place of the language digit.
When calls are set up to the test equipment, it is desirable
to avoid repetition of the request for the access code or for any
other digit. This is because the calls may come from equipment
which is not normally designed to interpret signals A-2, A-7
or A-8.
The address complete signal to be sent on calls to test equip-
ment must be one of the following:
- A-6 or A-3 followed by B-6 when incoming test
equipment is free,
- A-4 or A-3 followed by B-3 or B-4 when incoming
test equipment is busy.
Precautions should be taken that signal A-6 is only sent when
it is sure that the incoming test equipment is available for that
call. When receiving signal A-3, the outgoing test equipment sends
signal II-7 in response.
Note - In national working, or in international working where
the language digit is omitted by bilateral agreement, the following
multifrequency signals must be sent:
- I-13.
- Two digits "XY".
- I-15 (if necessary).
6.3.2 Test sequence for simplified test
The test sequence is as follows:
a) seizing of the automatic incoming test equip-
ment;
b) transition to answer state;
c) sending backward of a composite identification
signal 1020 + 1140 Hz; this signal will be acknow
ledged in a compelled manner by the signal mentioned under d);
d) recognition of a composite acknowledgement sig-
nal 1380 + 1980 Hz, sent in the forward direction;
e) on the disappearance of the acknowledgement sig-
nal the incoming test equipment passes to the clear-back state;
f ) on recognition of the clear-back signal, the
outgoing equipment will send in a normal manner the clear-forward
signal which will clear the connection and release incoming test
equipment. After release of the incoming line circuit the
release-guard signal will be sent in the normal way.
Detection of failure is made by timing out at the outgoing
equipment.
The frequencies mentioned under c) and d) are those for
System R2 interregister signalling; transmission and reception of
these frequencies in the incoming test equipment must be in accor-
dance with Section 4.
Attenuation pads may be inserted in the send and receive paths
of the outgoing test equipment to shift the receive level at the
input of the multifrequency receivers of the outgoing and incoming
test equipment toward the lower operational limit. This makes it
possible to diagnose abnormal loss on the circuit under test from
defective multifrequency signal exchange between outgoing and
incoming test equipment. For testing international System R2
circuits, the additional attenuation produced by the pads should be
10 _ 1 dB.
6.3.3 Good/no good transmission test equipment
In addition to the tests described in SS 6.3.1 and 6.3.2 a
good/no good transmission test may be provided as a simple means
for fast error localization. Such a test is described in
Recommendation Q.137 for System No. 4 (i.e. and the frequency of
the test signal, the tolerances and the deviation from the nominal
value, the test signal generators and receivers would all be the
same) but the sending level being -10 dBm.
It is to be noted that loop transmission measurements of the
kind specified in Recommendation Q.136 cannot be made on System R2
circuits.
6.4 Testing of analogue line signalling equipment under
abnormal conditions
The specification of the analogue line signalling equipment
contains clauses concerning operation under abnormal conditions,
including the action to be taken in case of interruption control
alarm. The testing equipment described in S 6.2 is not applicable
to such conditions and therefore the functioning of the analogue
line signalling equipment under abnormal conditions should be
tested internally at each end of a circuit either manually or
automatically with special equipment.
The detailed programme for this testing will be specified by
each Administration.
The design and construction of the line signalling equipment
should be such as to permit both operational and limit testing in
normal and abnormal conditions.
6.5 Alarms for the technical staff
Certain abnormal conditions in the signalling equipment should
cause alarms to be set off for the technical staff (see also
Recommendation Q.117). The relevant requirements are found in Sec-
tion 2 (line signalling equipment) and in Section 5 (time-out in
multifrequency registers).
As indicated in S 2.2.3, a fault occurring during release of a
circuit
may result in an abnormal blocking condition. In this case
there is a "tone-on" condition in both signalling directions, yet
the circuit is not in the idle condition since the release-guard
signal has not been received. If no special action is taken, a tem-
porary fault may therefore result in the circuit's being out of
service until it is manually restored by the maintenance staff,
after receipt of an alarm (see S 2.2.4).
It may accordingly be desirable to arrange for automatic res-
toration of abnormally blocked circuits. For Administrations wish-
ing to introduce this function, the recommended arrangement is
described below.
6.6 Recommended method for automatic restoration of an
abnormally blocked circuit
When an outgoing link is abnormally blocked, periodic sending
on the outgoing link of the seizing signal, followed shortly after-
wards by the clear-forward signal, is initiated.
Clearance of the fault which caused the abnormal blocked con-
dition will initiate a release-guard signal at the incoming end
whereupon the outgoing end restores the link to the idle condition.
The intervals, at which the periodic sequence described above
is repeated, should be between 30 seconds and 2 minutes.
The first operation of the automatic device should be per-
formed as soon as possible, but not before 2-3 seconds have
elapsed, after recognition of the abnormally blocked condition at
T1 (see S 2.2).
After a period of three to six minutes a delayed alarm should
be given in accordance with Recommendation Q.412, S 2.2.4.
In the event of a backward tone-off condition being detected,
other than in response to a periodic clear-forward signal, the
periodic sequence is suspended until the backward tone is again
recognized whereupon the periodic sending sequence is restarted.
If interruption control at the outgoing end occurs during the
abnormally blocked condition, the periodic sending sequence is
suspended until the interruption control reverts to normal, whereu-
pon the periodic sending sequence is restarted.
6.7 Instructions for the maintenance of channels and cir-
cuits using System R2 line signalling system at 3825 Hz
The analogue line signalling equipment specified in Section 2
is closely associated with the channel translating equipment and
its operation may be a function of the group and supergroup
translating and through-connection equipments. Maintenance of the
circuits and groups which support them is governed by the
principles and Recommendations of Volume IV. However, the introduc-
tion of out-band signalling calls for a few complements to these
Recommendations, as described below.
6.7.1 Bringing into service of group, supergroup, master-
group or supermastergroup links
a) SS 2.1 and 7.6 of Recommendation M.460
It should be noted that group and supergroup pilots placed at
140 Hz from a virtual carrier frequency are incompatible with sig-
nalling at 3825 Hz. Hence, the pilot on 84.140 kHz should not be
applied to groups in which channel 6 is to be operated with this
out-band signalling. Similarly, the pilot on 411.860 kHz should not
be applied to supergroups in which channel 1 of the group in the
group 3 position is to be operated with signalling at 3825 Hz.
If the channels of a group are to be operated with System R2,
each extremity of the group should be equipped, at the receiving
end, with a device to give protection against faulty signalling
conditions which may result from an interruption in the transmis-
sion channels (interruption control). This equipment, which is
based on pilot level detection; must comply with the conditions
specified in S 2.4.3 of Recommendation Q.416.
Note - If the channels of a supergroup which are operated
with System R2 have the same extremities as the supergroup, a dev-
ice based on monitoring of the supergroup pilot can be used instead
of one based on monitoring of the group pilot. It will have to meet
the same specifications.
b) S 7.2 of Recommendation M.460
The group-translating and through-connection equipments are
specified with a passband extending from 60.600 kHz to 107.700 kHz.
If it is wished to use channels 12 with signalling at 3825 Hz, it
is necessary to ensure when the group is set up, that the
corresponding frequency (60.175 kHz) is transmitted satisfactorily
from end to end of the group link.
Provisionally, in view of the operating margin of the receiv-
ing part of the signalling equipment, it is desirable to check that
attenuation at this frequency does not exceed the attenuation at
the group pilot frequency by more than 3 dB.
A similar precaution should be taken on setting up group links
when signalling is to be used at 3825 Hz on channel 12 of the group
transmitted in position 5 on the supergroup.
6.7.2 Setting-up and lining-up the channels of an interna-
tional group
6.7.2.1 Setting up the out-band signalling channel for the
System R2
Testing of the sending equipment:
- The sending level of the signalling frequency
corresponding to 3825 Hz if the carrier is taken as the frequency
of origin must be lined up at -20 _ 1 dBm0. When this frequency is
not to be sent, its leak transmitted to line should not exceed
-45 dBm0.
Testing of the receiving equipment:
- The signalling receiver must operate in the con-
ditions described in SS 2.3.2.1 and 2.3.2.2. It must not function
when a signal, of which the characteristics (level and frequency)
are such that the representative point is below the graph in
Figure 8/Q.415, is applied to the same point.
This test may be replaced by the following one to check the
protection against unwanted signals (impulsive noise):
- The sending part of the group terminal equipment
is connected to its receiving part by a closed-circuit loop at the
group distribution frame, this loop introducing a slight gain
(e.g. 3 dB)
if possible. The standardized click generator (see Figure 7/Q.414)
is applied to each speech channel successively at the point where
this channel is connected to the switching equipment, and a check
is made to ensure that no wrong signals are retransmitted at the
receiving end to the switching equipment by the channel signalling
equipment concerned or by those of the other channels in the group.
6.7.2.2 Closed-circuit loop tests: response time
When the transmission-reception loop of the terminal equipment
is effected at the group distribution frame or at an equivalent
point, a check is made to ensure that less than 30 ms elapse
between the moment when the change of condition is applied to the
transmitter associated with each channel and the moment when it
appears at the output of the corresponding receiver.
6.7.2.3 End-to-end tests
When the terminal channel-translating equipments are normally
connected to the extremities of the link, an end-to-end operating
test is carried out. The level of the line-signalling frequencies
transmitted and
received for each channel are likewise measured, to provide a
reference, at the group terminal distribution frames or at
equivalent points.
ANNEX A
(to Signalling System R2 Specifications)
(see Recommendations Q.400 and Q.441)
Provision of a forward-transfer signalling facility
A.1 General
The System R2 does not provide a forward-transfer line signal.
However for certain relations it may be decided by bilateral or
multilateral agreement to introduce the forward-transfer signalling
facility into System R2.
One possible procedure that has been adopted for use within
Europe, is to use the PYY in-band signal of System No. 4. This
solution is only economical in regions where the facility is needed
for a small proportion of the calls.
For international working the method as described below may be
followed.
Note - The method given in this Annex may also be adopted in
national networks where the forward-transfer facility is considered
necessary for trunk offering and recalling operators. However, care
must be taken to see that the transmission limits applying to the
forward-transfer signal specified are observed.
A.2 Method recommended for introducing the
forward-transfer signalling facility into System R2
Forward-transfer signalling will be provided by means of spe-
cial equipment which uses in-band signalling and which is switched
only on to those connections which may require this facility. The
amount of special equipment necessary can, accordingly, be reduced
to a minimum and adapted, in a flexible manner, to actual needs.
The in-band signal constituting the forward-transfer signal is sent
end-to-end between the outgoing and incoming international
exchanges. When the special equipment receives the
forward-transfer signal, it performs the necessary operations
at the incoming exchange.
A.2.1 Access to the special equipment in an incoming inter-
national exchange
In an incoming international exchange access to the special
equipment for forward-transfer signalling can be determined by the
use of the following indicators:
1) Special marking of incoming routes on which
forward-transfer signalling is used.
2) Language digit indicating semi-automatic
traffic.
3) Calls for code 11 or code 12 operator.
4) Special interregister signalling sequence in
which the incoming exchange sends signal A-5, send calling party's
category the forward-transfer signalling facility is required the
outgoing R2 register will respond to this by sending the
signal II-10. This signal indicates an operator-initiated call on
which special equipment for forward-transfer signalling is needed.
The use of these indicators will depend on the amount of
traffic for which forward-transfer signalling is employed. In some
cases one or two of the indicators will be utilized. In others,
combinations of all will be used to reduce to a minimum the amount
of special equipment required.
A.2.2 In-band forward-transfer signalling
In System R2 the in-band forward-transfer signal is the same
as that used in System No. 4. For the definition of this signal see
Recommendation Q.120, S 1.12. The signal is the signal PYY defined
in Recommendation Q.121, S 2.3. The forward-transfer signal is sent
in accordance with Recommendations Q.122 and Q.124.
The signal receiver and the splitting arrangements to be
incorporated in the special equipment at the incoming international
exchange are in accordance with Recommendations Q.123 and Q.124.
Provided it creates no difficulty for incoming national net-
work signalling, no splitting need be effected at the receiving end
and the caller will then hear the entire signal PYY.
MONTAGE: PAGE 144 = PAGE BLANCHE
PART IV
SUPPLEMENTS TO THE SERIES Q RECOMMENDATIONS
CONCERNING SIGNALLING SYSTEMS R1 AND R2
MONTAGE: PAGE 146 = PAGE BLANCHE
.bp
Supplement No. 1
LINE SIGNALLING FOR DC LINES WITH SYSTEM
R2 INTERREGISTER SIGNALLING
1 Introduction
In the following specification a line signalling system is
defined for 2-wire, DC-lines with or without metering facility dur-
ing speech.
The signalling polarity is provided by the incoming exchange
and a loop is provided in the outgoing exchange, so that in case of
cable fracture the outgoing exchange is informed automatically that
the line(s) concerned is(are) no longer available.
The line signal repertoire is based on the presence of
System R2 interregister signalling.
Apart from the metering pulses, the line signalling is con-
tinuous, which means that a certain state of a connection is
characterized by a
special signalling condition which is maintained as long as
the indicated condition continues to exist.
The following states are provided:
Forward direction:
1) idle
2) seized
3) clear-forward
Backward direction:
1) available
2) seized before answer
only without metering
only with metering
3) answered
4) metering
5) clear-back
6) forced release
7) not available (blocking)
2 Principles of the signalling and speech circuit
2.1 Signalling circuit
An example of a signalling circuit is shown in Figure 1. Feed-
ing of the loop occurs at the incoming exchange; the direction of
the current can be reversed by contacts X and the feeding current
can be switched off by contacts Tu. Contacts Bl are also used to
switch off the feeding current and consequently, to block the cir-
cuit. This can only take place if the line circuit in the outgoing
exchange is detected as being in the open or high resistance state.
When the contacts are in the position shown in the figure,
normal loop current flows and when the contacts X are switched over
reversed loop current flows.
In the outgoing exchange the state can be changed, by means of
contact W, from the high resistance condition with the
current-direction sensitive detector H switched in, to a state with
two low resistance current-direction sensitive detectors L and R.
In addition to contact W a contact K is provided to open the
loop; the open loop state is used to expedite the recognition of
clear-forward.
In the line circuit in the incoming exchange a filter is
needed to provide sufficient attenuation in the audible components
arising in case of polarity reversing. This is necessary, in par-
ticular, when metering pulses are sent during conversation.
In the line circuit in the outgoing exchange a filter may be
needed to provide sufficient attenuation in the audible components
arising when detectors L and R are operated and/or released. This
filter, if required at all, can normally be much simpler than the
one used in the incoming exchange.
2.2 Speech circuit
An example of a speech circuit is also shown in Figure 1. A
circuit equipped with the loop signalling system concerned has to
be electrically separated, from the preceding or following parts of
the connection. This prevents interference by longitudinal vol-
tages in other parts of the connection.
The detectors shall be of high impedance for speech.
Figure 1 p.
3 Meaning of the signalling states
In the Tables 1, 2 and 3 the meaning of the various signalling
states are shown.
Outgoing exchange:
- high resistance = idle
- low resistance = seized
- open = clear-forward.
Incoming exchange (without | etering):
- normal loop polarity = available, seized or
clear-back
- reversed loop polarity = unavailable or answer
- no voltage = unavailable (blocking).
Incoming exchange (with | etering):
- normal loop polarity = available or seized
- reversed loop polarity = unavailable or metering
pulse
- no voltage = unavailable (blocking) or forced
release.
4 Discrimination between the various signalling states
It is not necessary to be able to discriminate between each
state of one end and all states of the other end. However, the
capabilities shown in Tables 1, 2 and 3 should be provided.
Table 1 p.
Table 2 p.30
Table 3 p.
5 Operation (see Figures 2a-2f )
5.1 In the idle state the line circuit in the outgoing
exchange continuously checks whether or not the line is blocked by
the high resistance detector H. This detector operates when the
line is intact and the normal loop polarity is present in the
incoming exchange indicating the state "available".
Detector V in the incoming exchange is marginal and does not
operate in this state.
5.2 If the circuit in the outgoing exchange is seized for a
call the
exchange switches in the low resistance state and the low resis-
tance detector L operates.
In the line circuit in the incoming exchange the detector V
operates and the incoming equipment assumes the seized state.
5.3 The B-subscriber answers
a) Without metering
When the B-subscriber answers this is indicated by the
line circuit in the incoming exchange by reversing the loop feeding
polarity to reversed loop polarity. In the circuit in the outgoing
exchange the low resistance detector R operates and L releases.
b) With metering
When the B-subscriber answers this is indicated by the
incoming exchange (except in the case of a call that is free of
charge) by sending a metering pulse. The incoming exchange sends a
metering pulse by reversing the loop feeding polarity to reversed
loop polarity during the metering pulse.
In the line circuit in the outgoing exchange the low resis-
tance detector R operates and L releases.
5.4 The equipment must allow the following rules to be applied
with respect to the sending of metering pulses.
- A metering pulse must be completed by the incom-
ing exchange before sending forced release.
- After sending a metering pulse there is no
minimum period with normal loop polarity before forced release is
sent.
- During the receipt of a metering pulse the out-
going exchange is allowed to start sending clear-forward.
5.5 Backward release
a) Without metering
The incoming exchange can inform the outgoing exchange
that the B-subscriber has cleared by sending clear-back. This sig-
nal consists in reversing the loop feeding polarity to normal loop
polarity. In the line circuit of the outgoing exchange the low
resistance detector L operates and R releases.
The incoming exchange remains in this state (clear-back)
until the outgoing exchange sends clear-forward or the B-subscriber
reanswers.
b) With metering
The incoming exchange can inform the outgoing exchange
that the connection can be released by sending forced release. This
signal, which consists in switching off the loop feeding potential,
must persist for a minimum time T3. After receiving forced release
the line circuit of the outgoing exchange must transmit
clear-forward within a time T4 which is less than time T3.
Time T3 finishes when the line circuit in the incoming
exchange is again available; normal loop polarity is then sent.
The above mentioned cleard-forward in the line circuit in
the outgoing exchange is followed (just as in the case of the
release without forced release described in S 5.6 by the idle
state).
5.6 In order to release the circuit the outgoing exchange
opens the loop (clear-forward) during a time T1, before switching
in the high ohmic detector.
The incoming exchange must switch to one of the unavailable
states within a time T2 which is less than T1, unless the circuit
in this exchange is available before the time T2 has elapsed.
5.7 The incoming exchange can signal in two ways that it is
not available for a new call, namely by reversing the loop or by
switching off the feeding potentials.
In so far as the unavailability of the line circuit in the
incoming exchange forms part of normal operation, this state should
be indicated by reversed loop polarity.
Unavailability of the line circuit in the incoming exchange
for other reasons should be indicated by switching off the feeding
potentials.
5.8 If during the seized state of the line circuit in the out-
going exchange, the circuit is interrupted by disturbances or by
the feeding potential being switched off, the outgoing exchange has
to react to it in the same way as it does to clear-back (without
metering) or forced release (with metering), possibly followed by
blocking.
5.9 At the incoming exchange during the unavailable state and
for a subsequent period of 100 ms during the available state,
operation of detector V should be ineffective.
FIGURES 2 a)/b) p.5
FIGURES 2 c)/d) p.6
FIGURE 2 e) p.7
FIGURE 2 f) p.8
6 Time requirements
6.1 Recognition times
a) When the outgoing exchanges is in the idle
state but blocked the recognition time of the unblocking condition
(normal loop polarity) must be 100-300 ms.
b) In order to make a clear distinction between
the reversal of the polarity and no voltage the recognition time of
forced release must be 60-180 ms.
c) The recognition time of all remaining conditions
must be 10-40 ms.
6.2 Release times
a) The time T2 depends on the recognition time of
detector V and the reaction time of the incoming exchange which can
be assumed 30 ms; consequently the time T2 is defined 10-70 ms.
b) Without metering
The worst case when releasing a circuit occurs if the
B-subscriber releases just after the A-subscriber releases, causing
clear-back to be sent before the recognition time of clear-forward
has elapsed. In order to safeguard the operation in that particular
situation the time T1 is defined 300-600 ms.
c) With metering
The worst case when releasing a circuit occurs if within
the recognition time of clear-forward a metering pulse starts and
that within the length of this pulse clear-forward cannot be recog-
nized. In order to safeguard the operation in that particular
situation the time T1 is defined 500-1000 ms.
The time T3 depends on the discharge time of the involved
circuit and the time T4. For the discharge time, a time 80 ms can
be assumed. The time T4 depends on the recognition time of forced
release [see S 6.1 | )] and the reaction time of the outgoing
exchange which can be assumed 30 ms; consequently the time T4 is
defined 60-210 ms. Addition of these times leads to a
time T3 _" 300 ms.
6.3 Sending times
The length of the metering pulse to be sent shall be
120-180 ms.
7 Miscellaneous
This supplement does not describe values for the impedance of
the detectors and the cable and does not indicate
operate/nonoperate limits for the detectors, because these parame-
ter are rather dependent on the capabilities of the related net-
work. Therefore these requirements must be provided by each
Administration.
Supplement No. 2
BOTH-WAY WORKING OF THE ANALOGUE LINE
SIGNALLING VERSION OF SIGNALLING SYSTEM R2
1 Both-way working
In principle the Signalling System R2 is specified for one-way
working. The following additional clauses therefore apply only to
cases where Administrations have undertaken by bilateral agreement
to use both-way working.
Equipment which must be equally usable in both-way and in
one-way operation should be so designed that it can be easily
adapted to the requirements of either mode of operation.
A peculiarity of both-way working with the system under con-
sideration is that a blocking signal cannot be distinguished from a
seizing signal at either end of a circuit, since the transition of
the signalling condition corresponding to these signals is the
same, namely from tone-on to tone-off .
When a both-way circuit is seized simultaneously at both ends,
the signalling tone is disconnected in both directions of transmis-
sion; this is the criterion for detecting the double-seizure situa-
tion.
The special arrangements required for both-way working relate
to the two cases mentioned above. For all other signalling phases
the specifications for one-way working remain valid without modifi-
cation.
1.1 Normal conditions
1.1.1 Double-seizure
When the signalling equipment at one end of a both-way circuit
seizes that circuit by disconnecting the signalling tone, it must
verify that cessation of the signalling tone in the opposite direc-
tion does not occur within 250 _ 50 ms of the disconnection of the
signalling tone in the forward direction. If the signalling equip-
ment detects the removal of the signalling tone within that inter-
val then a double-seizure situation is recognized. Each end must
return to the idle state after sending the clear-forward signal and
recognizing tone-on condition on the signalling channel.
However, each end must, even if immediately seized for an out-
going call, maintain tone-on condition for at least 100 ms on the
outgoing signalling channel to ensure that the end of the double
seizure situation is recognized at the other end.
Although a double seizure has been recognized, the tone-off
| ondition in the backward direction is passed on backwards. This
will be regarded as an erroneous answer signal and lead to the
release of the connection in accordance with S 2.2.3 in the Specif-
ications. However, as
specified in S 1.2.1 below the clear-forward signal (tone-on
| ondition) must not be sent until the tone-off condition has been
maintained for at least 1250 _ 250 ms. Each end after sending of
the clear-forward signal returns to the idle condition when the
time interval 250 _ 50 ms (see S 2.2.2.6 in the Specifications)
has elapsed, and the sending of the tone-on condition from the
other end has been recognized.
In the sense of preventive action it is recommended that an
opposite order of circuit selection is used by each exchange of a
both-way circuit group to minimize double seizure.
1.1.2 Minimum duration of idle state after release-guard
When a both-way circuit is released, the end which acted as
the incoming end must, even if immediately seized for a call in the
opposite traffic direction, maintain the tone-on condition for at
least 100 ms to ensure that the release-guard sequence is recog-
nized at the other end.
1.1.3 Blocking
When a both-way circuit is blocked manually in its idle state
at one end (A), the blocking signal, must be transmitted to the
other end (B), where it will nevertheless be interpreted as a seiz-
ing signal. This will mean that an incoming R2 register is seized,
but is not receiving any interregister signal. After the lapse of
this register's time-out delay the circuit must be kept blocked
locally (at end B) against all calls in the B-A direction so long
as the tone-off condition persists in A-B direction.
To avoid certain difficulties (see SS 1.2.1 and 1.2.2 below)
and in contrast to S 2.2.3.5 in the Specifications the tone-off
condition is not applied in the opposite direction (B-A) to the
blocking direction (A-B).
When the blocking is removed at end A the signalling tone is
again transmitted in direction A-B and the B-end interprets the
onset of the signalling tone as a clear-forward signal, thereby
initiating the release-guard sequence in the B-A direction.
1.2 Abnormal conditions
The cases described below relate to interruption of the indi-
vidual signalling channels or to faults in the individual
line-signalling equipment. Interruption control does not function
in these cases.
In any circuit the interruption of one or both signalling
channels can bring about signalling sequences different from those
described in S 2.2.3 in the Specifications for one-way working.
1.2.1 When an interruption of the signalling channel in one of
the two directions brings about a signalling state corresponding to
blocking, the release-guard sequence will be initiated the moment
the interruption ends (see S 1.1.3).
The release-guard sequence implies that the signalling tone in
the backward direction be disconnected for an interval 450 _ 90 ms.
In both-way working this tone-off condition must not be interpreted
as seizing. To avoid a repetition of the exchange of release-guard
sequences certain precautions must be taken.
The following additional requirements should then be met:
- when the tone-off | ondition has lasted for an
interval of less than 750 _ 150 ms the return to tone-on condition
must not initiate a release-guard sequence;
- once the signalling condition corresponding to
seizing has been established, it must be maintained for at least
1250 _ 250 ms (this is a deviation to the requirement in S 2.2.2.1
in the Specifications).
When the interruption of one of the signalling channels has
brought about blocking of the circuit at one end (B), as described
above, that circuit can be seized at the other end (A). The end A
will not have received the blocking signal from end B (see S 1.1.3)
because that would cause permanent blocking of the circuit, which
would then no longer be able to restore itself to normal function-
ing. Should a seizing now occur, this will lead to loss of a call;
but subsequently, since the clear-forward signal cannot be
transmitted, the circuit will remain blocked at end A. The whole
further signalling sequence for reverting the circuit under
consideration to idle follows the specification for one-way cir-
cuits.
1.2.2 An interruption of both signalling channels on any cir-
cuit will be interpreted by the equipment at each end of the line
as seizing and the equipments will be blocked after the lapse of
the time-out delay of the incoming R2 registers.
If, after an interruption, only one signalling channel is
restored, the equipment at the incoming end in relation to that
signalling channel will interpret the tone-on condition as a
clear-forward signal and therefore bring into operation the
release-guard sequence. The terminal equipment at that end will
revert to the idle state, while the terminal equipment at the other
end remains blocked. This is the situation envisaged in S 1.2.1
above.
When both signalling channels are simultaneously restored, the
terminal equipment at both ends will interpret the onset of the
signalling tone as a clear-forward signal and this will bring the
release-guard sequence into operation. The result will be that the
terminal equipment at both ends will again recognize the tone-off
condition for a brief interval.
The following additional clause must be observed, to avoid
permanent blocking of the circuit in this condition:
- When, after blocking, the line-signalling equip-
ment at one end (A) of a both-way circuit has recognized the
clear-forward signal, it must complete the release-guard sequence
and restore the signalling tone after 450 _ 90 ms in the
direction A-B, even if the tone in direction B-A is interrupted. If
such interruption (in direction B-A) lasts for less than
750 _ 150 ms, the circuit returns to the idle state when the sig-
nalling tone is restored in both directions. If the interruption is
longer than 750 _ 150 ms, restoration of the signalling tone in
direction B-A will initiate a new release-guard sequence in
direction A-B (see S 1.2.1 above).
1.2.3 If an abnormal condition according to S 2.2.3.3 in the
Specifications occurs at one end of a both-way circuit, this end is
blocked for outgoing traffic. Such blocking should, however, not
prevent the circuit being used in the other traffic direction.
2 Special conditions regarding the interruption control for
both-way working
2.1 As soon as an operating condition has been established on
a both-way circuit and the outgoing and incoming ends of the cir-
cuit have been determined with certainty, the interruption control
specifications for one-way working become equally applicable to
both-way circuits.
2.2 When a both-way circuit is in the idle state, transition
to alarm of the interruption control of one direction of transmis-
sion must bring about operations to ensure that the signalling con-
dition existing at that moment on the signalling channel of the
opposite direction is maintained - in contrast to specifica-
tion 2.4.2.1 | ) | ) in the Specifications for one-way
working. This precaution obviates a permanent blocking of a
both-way circuit when interruption of the signalling channels
occurs simultaneously in both directions. It does not ensure
immediate blocking of the circuit; this will not occur until the
circuit has been seized by the next call.
2.3 In all operating conditions intermediate between the idle
| tate and the condition at the moment when the direction of
seizure of the both-way circuit is determined (see above), the
line-signalling equipment at both ends will be locked by interrup-
tion control in the condition in which it was before interruption
control passed to alarm.
Supplement No. 3
USE OF THE ANALOGUE LINE SIGNALLING VERSION
ON 2048 kbit/s PCM TRANSMISSION SYSTEMS
(refer to Recommendation G.732)
This solution is restricted for use within national networks
or internationally subject to bilateral agreements because it
requires some conventions which otherwise would have to be agreed
upon in CCITT. However, cost aspects may be a more decisive factor
than the required conventions.
The analogue version of the line signalling is used on both
the analogue and the digital transmission systems.
Two examples of the use of the analogue line signalling on
digital transmission systems are shown in Figure 1.
Apart from the interruption control handling, the transmulti-
plexer or other conversion equipment is transparent to the line
signalling.
The out-slot signalling is carried in time slot 16 of 2048
kbit/s systems (refer to Recommendation G.732, Table 3). Bit a of
time slot 16 is used to transmit the line signalling state of the
corresponding analogue channel. Bit b is used to indicate that the
analogue transmission system is in the alarm condition with the
following convention. For all the digital circuits connected to the
circuits of this analogue group bit b = 1 means alarm condition on
the analogue group.
1 In order to ensure the correct working of the line signal-
ling under fault conditions when employing T MUX some time require-
ments must be fulfilled.
1.1 The fault occurs on a PCM multiplex | see Figure 2)
If the fault occurs on PCM multiplex No. 1, the transmission
of the alarm indication will take place in the following time con-
ditions:
- the fault occurs at T ;
- the fault is detected by the transmultiplexer at
T + t1;
- the transmultiplexer stops sending the pilot on
GP1, GP2 and GP3at T + t1 + t2;
- the alarm indication is detected at the analogue
distant end at T + t1 + t2 + t3 + tp,
where:
- t1is the time needed for recognition of the
faulty transmission on a PCM 2048 kbit/s multiplex;
- t2is a processing time needed by the transmulti-
plexer after detection of alarm on the PCM multiplex;
- t3is the response time for the pilot receiver
when the pilot level falls: it is the time t v specified in
Recommendation Q.416 (t v < tr\ds | dm\di\dn + 13 ms), applicable
only for the recognition time t = 20 _ 7 ms;
- tpis the propagation delay on the analogue sec-
tion.
FIGURE 1 p.9
Figure 2, p.10
In the same situation, if the transmission fault disturbs sig-
nalling information, erroneous signals will be transmitted in the
following time conditions:
- the fault occurs at T ;
- the erroneous signalling condition appears at the
input of the analogue channel at T + t4;
- the erroneous signalling condition appears at the
input of the distant signalling equipment at T + t4 + t5 + tp,
where:
- t4is the time needed for transferring a line sig-
nal from digital access to analogue access;
- t5is the response time of the line signals
receiver at the distant analogue end (tr\dsin Signalling System R2
Specifications);
- tpis the propagation delay on the analogue sec-
tion.
If tris the recognition time of line signals specified in
Recommendation Q.412, correct working can be ensured if:
t1 + t2 + t3 + tp t4 + t5 + tp + tr
or
t1 + t2 + t3 t4 + t5 + tr
or
t1 + t2 + t v t4 + tr\ds + tr.
Recommendation Q.416 specifies that t v t rs | in. + t r
| in. (where t r | in. = 13 ms). Thus, if t1 + t2 t4, correct
working of line signalling can be ensured.
This inequality indicates simply that the time needed for
detection of a faulty transmission on a PCM multiplex plus the time
needed for stopping pilot sending when the alarm is detected must
be less than the transfer time of a line signal across the
transmultiplexer. This time requirement can be fulfilled, if neces-
sary, by introducing in the transmultiplexer a small delay in line
signals transmission.
1.2 The fault occurs on an analogue group
If, for example, the fault occurs on the analogue group GP1,
the transmission of the alarm indication will take place in accor-
dance with the following time conditions:
- the fault occurs at T ;
- the fault is detected by the transmultiplexer at
T + t1;
- bit b is set to 1 on the digital channels con-
cerned at T + t1 + t2;
- the alarm indication appears at the distant digi-
tal end at T + t1 + t2 + t3 + tp,
where:
- t1is the time needed for detection of loss of
pilot;
- t2is the time needed for transferring alarm
information to the digital output;
- t3is the response time of the signalling equip-
ment of the digital multiplex;
- tpis propagation delay.
If the same fault disturbs signalling information, erroneous
signals will be transmitted in the following time conditions:
- the fault occurs at T ;
- the erroneous signalling condition is detected by
the transmultiplexer at T + t4;
- bit a is changed at the sending end of the digi-
tal section by the transmultiplexer at T + t4 + t5;
- the erroneous signalling condition appears at the
input of the distant signalling equipment at T + t4
+ t5 + t6 + tp,
where:
- t4is the response time of the signalling tone
receiver in the transmultiplexer;
- t5is the time needed for transferring a line sig-
nal from the output of the signalling tone receiver to the digital
output (change of bit a );
- t6is the response time of the signalling equip-
ment of the PCM 2048 kbit/s multiplex (t3 = t6).
Correct working of line signalling is ensured if:
t1 + t2 + t3 + tp t4 + t5 + t6 + tp + tr
or
t1 + t2 t4 + t5 + tr
and if trhas its minimum value t1 + t2 t4 + t5 + 13 ms.
This inequality indicates that the time for detecting loss of
pilot plus the time needed for setting bit b to 1 after loss of
pilot detection by the transmultiplexer must be less than the
response time of the signalling tone receiver in the transmulti-
plexer plus the transfer time of line signal plus 13 ms.
Supplement No. 4
IN-BAND LINE SIGNALLING FOR 3 kHz SPACED CHANNELS
1 Line signalling code
1.1 General
For 3 kHz spaced carrier circuits, an in-band line signalling
system is necessary. For this purpose the line signalling of Sig-
nalling System No. 4 (Recommendations Q.121, SS 2.1, 2.2, 2.3
and Q.122) must be used.
1.2 Line signals
The following line signals of Signalling System No. 4 are
necessary in combination with Signalling System R2 interregister
signalling.
1.2.1 Forward signals
- Terminal seizing: in case of transit this is
indicated by the interregister signalling;
- Forward-transfer: although the forward-transfer
facility is not provided in Signalling System R2, it can be used
when Recommendation Q.400, S 1.1.3 is implemented;
- Clear-forward.
1.2.2 Backward signals
- Answer,
- Clear-back,
- Release-guard,
- Blocking,
- Unblocking: this signal is not separately defined
in the Specifications of Signalling System R2, but it is similar to
restoring the tone (see Recommendation Q.412, S 2.2.2.5).
Supplement No. 5
LINE SIGNALLING (ANALOGUE VERSION) WITH METERING
1 General
Signalling System R2 may be used as an integrated signalling
system for national and international traffic in a national net-
work. Under certain conditions it is desirable to have additional
line signals available, and in particular a metering signal in
order to permit the charging of national calls and international
calls generated in the national network concerned.
This supplement to the specifications of Signalling System R2
deals only with the clauses for exchange line signalling equipment
which has been changed in order to take care of the addition of new
operating conditions created by the additional metering signals and
related only to the requirements of a national network. The condi-
tions of the interruption control have been adapted accordingly.
The transmission of the metering signal can be extended over a
maximum of three links between the subscriber exchange and the
exchange where the charging equipment has been installed.
2 Line conditions
Taking into account the time sequence, the circuit will have
the seven characteristic operating conditions shown in Table 1.
TABLE 1 p.
3 Clauses for exchange line signalling equipment
3.1 Recognition time for transition of signalling condition
The recognition time for a changed condition (transition from
tone-on to tone-off or vice versa) is 40 _ 10 ms according to the
decisions taken by Study Group XI of the CCITT. The definition of
the recognition time is indicated in Recommendation Q.412, S 2.2.1.
3.2 Normal operating conditions
3.2.1 General
Except for the states, metering and forced release, the other
states (seizure, answered, release, blocking and release-guard)
follow the same states as those indicated in Recommendation Q.412,
S 2.2.2. Instead of the situation "release in clear-back state" a
situation "release in forced release state" is possible.
3.2.2 Metering
The metering signals are pulse-type signals transmitted back-
wards during the conversation on a link-by-link basis. They are the
only signals for which a repetition of the actual signal in a
link-by-link basis is necessary in order to avoid an inacceptable
distortion of the metering signals.
For the meter pulses the following limits have to be
respected:
- sending: 120-180 ms;
- recognition time between the recognized transi-
tions at the receiving side: 60-90 ms.
For the interval between metering signals, the following send-
ing limit has to be observed: minimum 300 ms.
The time at the sending end between the answer signal and the
start of the first metering signal and between the end of the last
metering signal and the start of the forced release signal shall be
more than 300 ms.
3.2.3 Forced release | see Figures 1 and 2)
When the called subscriber clears at the end of a call, the
exchange which controls the connection will receive the clear-back
signal from the called subscriber's end. If the calling subscriber
does not clear within a period defined by the Administration con-
cerned for national traffic, and according to Recommendation Q.118
for international traffic, the controlling exchange stops metering,
transmits forced release to the preceding exchange and clears for-
ward the succeeding part of the connection. In the preceding
exchange, the forced released signal will only be recognized after
300 ms or more in order to avoid confusion with a metering signal.
After recognition of the forced release signal in the ori-
ginating exchange, the tone-on condition will be transmitted for-
wards and the part of the connection to the controlling exchange
will be released.
The release procedure is identical to the one specified for
the analogue version of the line signalling.
There is no forced release in case of no reception of the
answer signal in the controlling exchange following an
address-complete signal. After a period defined by the Administra-
tion concerned for national traffic, and according to
Recommendation Q.118 for international traffic the controlling
exchange sends busy tone to the calling subscriber and sends
clear-forward to release the succeeding part of the connection.
Figure 1 p.
Figure 2 p.
4 Mode of operation of interruption control
4.1 General
Generally speaking, it can be said that the mode of operation
of the interruption control complies with the specifications of
Signalling System R2, and in particular with Recommendation Q.416.
However, it is necessary to define the work of operation of the
interruption control for the following conditions:
a) circuit in answered state (metering in the back-
ward direction);
b) circuit in forced release state.
4.2 Mode of operation of interruption control at the incom-
ing end (transmission interrupted in the forward direction)
a) Circuit in answered state
Transition of interruption control to alarm brings about:
i) locking of the sending unit in its position,
i.e. in the tone-off condition; if, at the moment of operation of
interruption control the tone-on condition existed on the backward
direction (metering signal), it will be locked in the tone-off con-
dition;
ii) locking of the receiving unit in its position,
i.e. in the tone-off condition.
The other conditions are also in agreement with the specif-
ications described in Recommendation Q.416, S 2.4.2.1 | ).
b) Circuit in forced release state (transmission of
forced release signal in backward direction)
Transition of interruption control to alarm brings about:
i) locking of the sending unit in its position,
i.e. in the tone-on condition;
ii) locking of the receiving unit in its position,
i.e. in the tone-off condition;
iii) immediate release of the part of the connec-
tion beyond faulty circuit (including the called subscriber's
line).
The conditions are similar to the specifications described
in Recommendation Q.416, S 2.4.2.1 | ), "clear-back state".
4.3 Mode of operation of the interruption control at the
outgoing end (transmission in the backward direction interrupted)
a) Circuit in answered state
In this case, transition of the interruption control to
alarm does not cause immediate action. A clear-forward signal sent
on the part of the connection preceding the faulty circuit must be
repeated forward to ensure that, if the forward signalling channel
is left intact, the part beyond the faulty circuit is cleared.
Once the interruption control reverts to normal, the con-
nection is maintainted provided the caller and the called sub-
scriber are still holding. On the other hand, by the time the
interruption control reverts to normal, the clear-forward signal
may already have been sent and the situation will be the one
described under circuit seized but not in answered state.
b) Circuit in forced release state (transmission
forced release signal in backward direction)
Transition of interruption control to alarm causes locking
of the receiving unit in its position, i.e. the tone-on condition.
The procedures are similar to those in the position "clear-back
state" in the specifications of the analogue version of the line
signalling, Recommendation Q.416, S 2.4.2.2 b).
Supplement No. 6
LINE SIGNALLING (DIGITAL VERSION) WITH METERING
1 Introduction
Signalling System R2 line signalling, digital version, is a
line signalling system for use over digital line transmission
equipment conforming to Recommendation G.732.
For many national applications it is desirable that the digi-
tal version has additional line signals available to enable the
charging of calls.
This supplement proposes possible solutions to provide for
charging of calls, namely the provision of a meter signal and a
forced release signal.
2 Signal codes
The signalling codes are given in the Table 1 below.
H.T. [A/T1]
TABLE 1
__________________________________________________________
Signalling Code
State of the circuit Forward Backward a f
__________________________________________________________
Idle/released 1 0 or 1 or 0
Seized 0 0 or 1 or 0
Seizure acknowledged 0 0 or 1 or 1
Answered/meter 0 0 or 0 or 1
Meter/seizure acknowledged 0 0 or 1 or 1
Clear-forward 1 0 or 0 or 1
or 1 or 1
or 0 or 0
Forced release 0 0 or 0 or 0
Blocked 1 0 or 1 or 1
__________________________________________________________
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Table [A/T1], p.
3 Choice of meter codes
Some line signalling systems indicate a meter pulse by a sig-
nal identical to a "pulsed clear-back", signal. In this cir-
cumstance for ease of signal conversion ab = 1, bb = 1, which nor-
mally indicates clear-back, may be used to represent a meter pulse.
Other signalling schemes however use a "pulsed answer" signal to
indicate a meter pulse. In this circumstance ab = 0, bb = 1 may be
used to represent a meter pulse.
4 Clauses for exchange line signalling equipment
4.1 Normal operating conditions
The following operating conditions apply in addition to those
described in Recommendation Q.422.
4.1.1 Meter: | etering signals are pulse type signals
transmitted backwards during the conversation from the call charg-
ing point to the subscriber's call meter in the originating
exchange.
In the case of "pulsed clear-back" meter pulses, a pulse is
indicated by a change from the answer (ab = 0, bb = 1) signal to an
ab = 1, bb = 1 signal and then a change back to ab = 0, bb = 1. To
avoid confusion between meter pulses and clear-back the use of
clear-back is not allowed.
In the case of "pulsed answer" meter pulses, a pulse is indi-
cated by a change of ab = 1, bb = 1 to ab = 0, bb = 1 and back to
ab = 1, bb = 1. The first pulse indicates answer, it may also indi-
cate a meter pulse. A clear-back signal is not provided.
Meter pulses must be longer than 30 ms to ensure recognition
at the outgoing end.
4.1.2 Forced release: | rior to answer and after a period
defined by the Administration concerned for national traffic and
according to Recommendation Q.118 for international traffic, the
charge controlling exchange transmits the forced release signal to
the preceding exchange and clears forward the succeeding part of
the connection. When the called subscriber clears at the end of a
call, the exchange which controls call charging will receive the
clear-back signal from the called subscriber's end. If the calling
subscriber does not clear within a period defined for national
traffic by the Administration concerned and for international
traffic according to Recommendation Q.118, the charge controlling
exchange stops metering, transmits the forced release signal to the
preceding exchange and clears forward the succeeding part of the
connection. A forced release signal is indicated by a change to
ab = 0, bb = 0.
On recognition of forced release in a preceding exchange the
connection is released, the forced release signal repeated to any
other preceding exchanges, and a clear forward signal sent on the
link. The succeeding exchange, on receipt of the clear forward,
returns an idle signal and returns the link to the idle state.
Figure 1 shows line signals for a sequence of meter pulses
followed by forced release in the case of "pulsed clear-back" meter
pulses.
4.2 Actions appropriate to various signalling conditions
Tables 2 and 3 indicate the states appropriate to each signal-
ling code recognized and the actions to be taken at the outgoing
and incoming ends respectively.
Figure 1, p.15
H.T. [A/T2]
TABLE 2
Outgoing end
______________________________________________________________________________________________________________________________________________________________________
Received code
{
a b = 0, b b = 0 a b = 0, b b = 1 a b = 1, b b = 0 a b = 1, b b = 1
______________________________________________________________________________________________________________________________________________________________________
Idle/released a f = 1, b f = 0 Abnormal, see Note 1 Abnormal, see Note 1 Idle Blocked
______________________________________________________________________________________________________________________________________________________________________
Seized a f = 0, b f = 0 Abnormal, see Note 2 Abnormal, see Note 2 Seized, see Note 2 Seizure acknowledged
______________________________________________________________________________________________________________________________________________________________________
Seizure acknowledged a f = 0, b f = 0 Forced release Answered/ meter Abnormal, see Note 3 Seizure acknowledged
______________________________________________________________________________________________________________________________________________________________________
{
Answered | ua)/meter | ub)
} a f = 0, b f = 0 Forced release Answered/ meter Abnormal, see Note 4 Meter/seizure acknowledged
______________________________________________________________________________________________________________________________________________________________________
{
Meter | ua)/seizure acknowledged | ub)
} a f = 0, b f = 0 Forced release Answered/ meter Abnormal, see Note 4 Meter/seizure acknowledged
______________________________________________________________________________________________________________________________________________________________________
Forced release a f = 0, b f = 0 Forced release, see Note 5 Abnormal, see Note 5 Abnormal, see Note 5 Abnormal, see Note 5
______________________________________________________________________________________________________________________________________________________________________
Clear-forward a f = 1, b f = 0 Clear-forward Clear-forward Released = Idle Clear-forward
______________________________________________________________________________________________________________________________________________________________________
Blocked a f = 1, b f = 0 Abnormal, see Note 1 Abnormal, see Note 1 Idle Blocked
______________________________________________________________________________________________________________________________________________________________________
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a) Used for "pulsed clear-back" meter pulses.
b) Used for "pulsed answer" meter pulses.
Note 1 - In these conditions the outgoing end must prevent a new
seizure of the circuit. A delayed alarm should also be given.
Note 2 - Non-recognition of the seizing acknowledgement signal
100-200 ms after sending the seizing signal on a terrestrial link
or 1-2 seconds after sending the seizing signal on a satellite link
results in an alarm and either congestion information being sent
backward or a repeat attempt being made to set up the call. The
outgoing end must prevent a new seizure of the circuit. When the
seizure acknowledgement signal is recognized after the time-out
period has elapsed, the clear-forward signal must be sent.
Note 3 - Receipt of a b = 1, b b = 0 by the outgoing switching
equipment for 1-2 seconds after recognition of the seizing ack-
nowledgement signal and prior to recognition of the answer signal,
results in an alarm and either congestion information being sent
backward or a repeat attempt being made to set up the call. The
outgoing end must prevent new seizures of the circuit. When b b
reverts to 1 after the 1-2 seconds time-out period has elapsed, the
clear-forward signal must be sent.
Note 4 - In the case of recognition of a b = 1, b b = 0 whilst in
the answered state, immediate action is not necessary. On receipt
of clearing from the preceding link, the clear-forward signal (a
f = 1, b f = 0) must not be sent until b b is restored to 1.
A delayed alarm should also be given.
Note 5 - After forced release is recognized, the outgoing switch-
ing equipment must be released and then the idle signal (a f = 1, b
f = 0) sent on the link. The outgoing end must prevent a new
seizure on the circuit until the link returns to the idle state
upon reception of a b = 1, b b = 0. The forced release signal must
be sent on the preceding link (if any).
Tableau [A/T2], p.16
Blanc
H.T. [A/T3]
TABLE 3
Incoming end
_________________________________________________________________________________________________________________________________________________________________________________
Received code
{
a f = 0, b f = 0 a f = 0, b f = 1 a f = 1, b f = 0 a f = 1, b f = 1
_________________________________________________________________________________________________________________________________________________________________________________
Idle/released a b = 1, b b = 0 Seized Fault, see Note 1 Idle Fault, see Note 1
_________________________________________________________________________________________________________________________________________________________________________________
Seizure acknowledged a b = 1, b b = 1 Seizure acknowledged Fault, see Note 2 Clear-forward Fault, see Note 2
_________________________________________________________________________________________________________________________________________________________________________________
{
Answered | ua)/meter | ub)
} a b = 0, b b = 1 Answered/ meter Fault, see Note 3 Clear-forward Fault, see Note 3
_________________________________________________________________________________________________________________________________________________________________________________
{
Meter | ua)/seizure acknowledged | ub)
} a b = 1, b b = 1 Meter/seizure acknowledged Fault, see Note 3 Clear-forward Fault, see Note 3
_________________________________________________________________________________________________________________________________________________________________________________
Forced release a b = 0, b b = 0 Forced release Fault, see Note 8 Clear-forward see Note 4 Fault, see Note 8
_________________________________________________________________________________________________________________________________________________________________________________
Clear-forward {
a
b = 0, b
b = 1
or
a
b = 1, b
b = 1
} Abnormal seized see Note 7 Fault, see Note 7 Clear-forward see Note 7 Fault, see Note 7
_________________________________________________________________________________________________________________________________________________________________________________
Blocked a b = 1, b b = 1 Abnormal seized see Note 5 Fault, see Note 6 Blocked Fault, see Note 6
_________________________________________________________________________________________________________________________________________________________________________________
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a) Used for "pulsed clear-back" meter pulses.
b) Used for "pulsed answer" meter pulses.
Note 1 - When in the idle/released state b f changes to 1, b b
must be changed to 1.
Note 2 - In these cases a timeout device is started which after a
certain interval clears the connection beyond the faulty circuit:
this timing arrangement may be the one specified in
Recommendation Q.118, S 4.3.3. If the answer signal is recognized
during the timeout delay, the timer is stopped but the answer sig-
nal is not sent on the preceding link until recognition of a
f = 0, b f = 0. If the clear-back signal is recognized while the
fault persists, the connection beyond the faulty circuit must be
released immediately. Additionally, when the incoming register has
not started to send the last backward signal, the rapid release
procedure described in Note 5 may be used.
Note 3 - In these cases no action is taken until the forced
release signal or the clear-back signal (if the exchange is the
call metering control point) is recognized, at which stage the con-
nection beyond the faulty circuit is immediately released and the
forced release signal sent to the preceding exchange.
Note 4 - After a f = 1, b f = 0 is recognized, the circuit is
returned to the idle state by sending a b = 1, b b = 0.
Note 5 - In this case, immediate action is not necessary. However,
rapid release of the circuit should occur if the incoming end simu-
lates answer by sending a b = 0, b b = 1.
Note 6 - Under these conditions no action is taken.
Note 7 - After clear-forward signal is recognized and until the
code a b = 1, b b = 0 is sent, all transitions in the forward
direction shall be ignored.
Note 8 - The circuit is kept in the forced release state until a
f = 1, b f = 0 is recognized.
Tableau [A/T3], p.17
Blanc
5 Protection against the effects of faulty transmission
5.1 Introduction
When faulty transmission conditions in PCM systems are
detected both PCM terminals apply the state corresponding to state
1 on the PCM line on each "receive" signalling channel at the
interface with the switching equipment, as indicated in Table 4 of
Recommendation G.732. In this way the incoming switching equipment
receives the equivalent af = 1, bf = 1 on the PCM line and the
outgoing switching equipment receives the equivalent of ab = 1,
bb = 1.
5.2 Incoming switching equipment
At the incoming end a PCM fault results in af = 1, bf = 1: so
this fault can be identified and appropriate actions according to
Table 3 can be taken.
5.3 Outgoing switching equipment
At the outgoing end a PCM fault results in ab = 1, bb = 1.
Two cases are to be considered:
a) Meter pulses are indicated by ab = 0, bb = 1
A fault results, as it is stated in Table 2, in a blocked
state or seizure acknowledged state. This means that all circuits
in the idle state of a faulty PCM multiplex will be blocked and
that seized circuits will go to or remain in the seizure ack-
nowledged state.
b) Meter pulses are indicated by ab = 1, bb = 1
A PCM fault will result in the recognition of a meter
pulse each time a failure appears. To avoid this recognition, the
outgoing switching equipment must handle the service alarm informa-
tion given by the PCM terminal equipment in a separate way.
When the outgoing switching equipment detects a service
alarm information it must block the detection of signalling transi-
tions to avoid recognition of erroneous signalling codes caused by
the failure.
The reception of a clear-forward signal on the preceding
link or the detection of the calling subscriber's release will
cause, after the end of the PCM failure, the sending of a
clear-forward signal on the succeeding part of the connection.
6 Bothway working
The additions described in this contribution do not affect the
suitability of the digital version for bothway use.
Supplement No. 7
SEMI-COMPELLED AND NON-COMPELLED MULTIFREQUENCY INTERREGISTER
SIGNALLING FOR NATIONAL SATELLITE APPLICATIONS BASED ON SYSTEM
R2
INTERREGISTER SIGNALLING
1 Introduction
1.1 The Semi-Compelled and Non-Compelled Multifrequency Sig-
nallings, herein specified and based on Signalling System R2
(Fully-Compelled Signalling), make use of a pulse signal sending
procedure and are supposed to increase signalling speed on national
satellite circuits. Their application is restricted to those cases
in which the consequences of increased propagation times over
Fully-Compelled Signalling may bring about insolvable technical
problems for the national network, may make impossible the reten-
tion of the information capabilities and facilities provided by
that signalling or may make rather expensive the operation of cir-
cuits.
This may occur in national networks which have a large number
of satellite circuits, e.g. when national satellites are used.
1.2 Parameters related to operation of national networks may
be affected by great increase in satellite propagation time, com-
pared with the terrestrial value, such as:
- increase in the holding times of the telecommuni-
cations network;
- increase post-dialling delay;
- increased amount of equipment to handle the same
traffic and consequently larger space taken up by equipment;
- the maximum capacity of exchanges is reached at
lower traffic values.
The negative effect over those parameters implies a loss in
service quality and an increase in investments made in national
networks.
Better performances may be obtained through the Semi-Compelled
Multifrequency Signalling, which speeds up the process of inter-
change of signals via satellite.
1.3 In some cases, the characteristics of national networks
where the features of the Signalling System R2 are fully used may
require that the process of interchange of signals via satellite
must be still more accelerated so that delays may be kept within
certain limits, otherwise those characteristics should be changed.
Some of the said characteristics are the following:
- time-out requirements;
- routing plan;
- charging method;
- sending of complete calling subscriber number
(total identification of calling subscriber);
- information about called subscriber condition by
means of Group B signals, instead of simple Address-Complete signal
(signal A-6);
- traffic restriction through analysis of calling
subscriber category in destination (Group II signal in acknowledge-
ment to signal A-3).
Relative to the above-mentioned cases, the choice falls on the
Non-Compelled Multifrequency Signalling which allows a substantial
increase in speed as regards signal interchange.
1.4 Unlike the Fully-Compelled Multifrequency Signalling, the
Semi-Compelled and Non-Compelled Signal lings here described permit
that, within certain particular limitations, the characteristics,
facilities and mode of operation (including network management)
already existing in the national networks which use Signalling
System R2 may be maintained, making possible the operation of
satellite circuits with an information interchange rate similar to
that of Signalling System R2 which operates on the terrestrial
links.
2 Line signalling
The line signalling to be used together with the Non-Compelled
Interregister Signalling must include a Proceed-to-Send signal.
All remaining signals may be used in the original form.
As for digital circuits, line signalling-digital version of
Signalling System R2 may be fully used. The seizing acknowledgement
signal in this application is used as Proceed-to-Send indication.
A pulsed line signalling which presents an excellent perfor-
mance over terrestrial or satellite links and can be used with
Non-Compelled Signallings is specified in S 4.
3 Interregister signalling
3.1 General
The Semi-Compelled and Non-Compelled Multifrequency Signal-
lings here specified basically show the same characteristics and
facilities existing in the Fully-Compelled Multifrequency Signal-
ling used with Signalling System R2, except, obviously, the way of
sending and receiving MF signals.
This Supplement specifies only the characteristics and facili-
ties which differ from those foreseen in Specifications of Signal-
ling System R2 and the meanings of some signals which are used in
a different way from that system.
3.2 Semi-Compelled Signalling
3.2.1 Introduction
The Semi-Compelled Signalling over satellite links can be usu-
ally used in the end-to-end method, between the signalling equip-
ment of the origin of the call and the signalling equipment at the
incoming end of the satellite link, as recommended in Specifica-
tions of Signalling System R2 except when, for charging or manage-
ment reasons, the signalling equipment at the outgoing end of the
satellite link is not released until the complete setting-up of the
call.
The pulsed form of sending backward signals (Groups A and B)
is the only difference that such signalling presents in relation to
Specifications of Signalling System R2.
3.2.2 Pulse duration
As regards backward signals, pulse duration corresponds to
100 _ 20 ms.
3.2.3 Composition of the Groups of Signals I and II (for-
ward) and A and B (backward) and Meaning of the Signals
The composition of the Groups of Signals and their respective
meanings are thoroughly identical with those foreseen in Signalling
System R2, as well as combinations of frequencies which form the
various signals.
3.2.4 Build-up and Time Specifications of a Complete For-
ward Semi-Compelled Signalling Cycle
Figure 1 shows in detail the build-up and time sequence of a
semi-compelled signalling cycle.
If the values of T int | and T int | lie within certain lim-
its, they do not contribute to the total duration of the
semi-compelled signalling cycle, as can be seen from Figure 1.
Then, the total duration TS\dCof a complete semi-compelled signal-
ling cycle is given by the formula:
T SC = T PF + T PB +
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T ` R D + T ` O A
fIT dR D + T O A
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+ T int | + T S 1
D + T S 1 A + T P or
The subscripts D and A apply respectively to the outgoing and
the incoming registers.
Considering the values established in Recommendation Q.457,
S 4.5.2 and assuming that:
T S
1
D
+
T S
1
A
= T S
1
+ T S
2
and T P =
100 _ 20 ms,
the probable extreme values of the semi-compelled signalling cycle
TS\dCwould be:
620 ms TS\dC 840 ms
3.2.5 Call routing procedures
Whenever technically feasible, the overlap method may be used
for call routing.
The Semi-Compelled Signalling is applied just like the
Fully-Compelled Signalling (System R2), though there are minor res-
trictions towards its use on satellite channels.
3.2.6 Other characteristics of the Semi-Compelled Signal-
ling
As concerns other characteristics related with the signalling
(Multi-frequency Signalling Equipment, Time and Transmission
Requirements, etc.), Specifications of Signalling System R2 are
applicable.
3.3 Non-Compelled Signalling
3.3.1 Introduction
The Non-Compelled Signalling over satellite links is used in
the link-by-link method between signalling equipment correspondent
to the outgoing and incoming ends of the satellite link.
The basic differences that such signalling shows in relation
to Specifications of Signalling System R2 are the way of sending
signals in both directions (those forward and backward signals are
sent in the form of pulses) and the non-existence of Group A of
Signalling System R2.
3.3.2 Pulse duration and minimum pulse interval
Pulse duration corresponds to 100 _ 20 ms for both forward and
backward signals.
The minimum interval between two consecutive forward pulses is
100 _ 20 ms.
3.3.3 Composition of the Groups of Signals (I, II and B)
and Meaning of the Signals
3.3.3.1 General
The Non-Compelled Signalling is composed of the Groups of
Signals I and II (forward signals) and B (backward signals)
correspondent to the same Groups as those of Signalling System R2.
The Group A of backward signals of Signalling System R2 is
unnecessary by the following reasons:
- The signalling equipment at the incoming end of
the satellite link operates as storage point for information coming
from the origin and operates without sending via satellite the sig-
nals A-1, A-2, A-3, A-5, A-7, A-8, A-11, A-12, A-13 and A-14.
- The meaning of signal A-4 is transferred to
Signal B-9 (spare for national use in the Fully-Compelled Signal-
ling System R2).
- The use of signal A-6 is not required. Signals
of Group B can be used. In case it is necessary to use the meaning
of A-6, it can be allocated to Signal B-10 (spare for national use
in the Fully-Compelled Signalling System R2).
- Signals A-9 and A-10 are spare for national use
in the Fully-Compelled Signalling System R2.
The Groups of Signals I, II and B maintain the same structure
(including the same frequency combinations) as that used in the
Fully-Compelled Signalling System R2, using the same signalling
senders and receivers.
Some modifications, exclusions or inclusions in the meaning of
some signals in relation to the Fully-Compelled Signalling
System R2 allow the Non-Compelled Signalling the following facili-
ties:
- Sending of category and number of calling sub-
scriber, through positioning of Signals I-12 and I-15 respectively
before and after the sending of this complete information. Category
information can be transmitted only through that same procedure.
Such a method for sending the calling subscriber category and
number by means of Signals I-12 and I-15 is carried out in a
predetermined sequence between two successive digits of the
transmission of the called subscriber number.
3.3.3.2 Meaning of the signals for national use
Only the signals which have shown some variation in relation
to their usual meanings in the Fully-Compelled Signalling System R2
are presented next.
3.3.3.2.1 Group I forward signals
I-12 It indicates that only the category or the category
and the number of the calling subscriber will follow.
I-13 a) Test call indicator.
b) Access to test equipment (code 13).
Both a) and b) have the same meanings as those of the
Fully-Compelled Signalling System R2. The meaning "Satellite Link
not Included" was deleted.
3.3.3.2.2 Group B backward signals
B-9 Congestion in the national network (before changeover
from Group A signals to Group B signals in the Fully-Compelled Sig-
nalling System R2) or if time-out in the signalling equipment at
the destination end of the satellite link has occurred.
B-10 Address-complete, charge, set-up speech conditions
(only if destination equipment of the national network cannot send
the usual end-of-selection signals).
3.3.4 Configurations of the signalling network
The Non-Compelled Signalling may be basically used:
a) Between the Signalling Equipment of two Switch-
ing Exchanges (Translation Points coincide with Switching Points).
Signalling equipment of switching exchanges located at both
ends of the satellite links must be able to send and receive
Non-Compelled Signalling, as illustrated in Figure 2.
For that configuration, adequate functional changes are
required in the signalling equipment of those switching exchanges.
b) Between Signalling Translation Equipment
separated from the Switching Exchanges (Translation Points do not
coincide with Switching Points).
Signalling Translation Equipment is independent of signal-
ling equipment of switching exchanges. It may be installed near
those exchanges or in separate places, as illustrated in Figure 3.
For that configuration, there is not any change in any
equipment of the national network, and the introduction of signal-
ling translators may be carried out just through the simple inter-
connection with distribution frames.
Note - A combined solution is also possible.
3.3.5 Call routing procedures
3.3.5.1 Relative to the starting point
There are no restrictions for applying the overlap method when
using the Non-Compelled Signalling.
There are two main kinds of calls:
a) Calls for subscribers from a national (or inter-
national) numbering area different from that of the calling sub-
scriber.
The national (or international) prefix and code are to be
dialled.
b) Calls for subscribers from the same numbering
area as that of the calling subscriber.
The national (or international) prefix and code are not to
be dialled, but only the subscriber number.
In both cases a) and b), the starting point at the Signalling
Translation Point at the outgoing end of the satellite link occurs
after reception of the sufficient number of digits to route the
call.
If configuration presented in S 3.3.4 b) (Signalling Transla-
tion Equipment separated from the Switching Exchanges) is adopted,
signals may be sent forward as soon as they are received by the
Signalling Translation Equipment at the Signalling Translation
Point.
3.3.5.2 Relative to the sending sequence of Group I and II
forward signals
The main cases concerning the sending sequence of
non-compelled signals are the following:
a) Calls with complete identification of the cal-
ling subscriber number (i.e. for centralized toll ticketing).
After reception of a sufficient number of digits of the
called subscriber number to route the call, they may be sent en
bloc . Then, there is the sending of category and number of cal-
ling subscriber, which are preceded and followed by signals I-12
and I-15, respectively. Such signals can also be sent en bloc if it
does not contribute to delay routing procedures. After reception of
signal I-15, the digits of the called subscriber number continue to
be sent so far as they are dialled and available for sending (over-
lap method).
A scheme corresponding to national calls is shown in Fig-
ure 4.
b) Calls without complete identification of the
calling subscriber number.
After reception of a sufficient number of digits of the
called subscriber number to route the call, they may be sent en
bloc . Then, there is the sending of the calling subscriber
category, which is preceded and followed by Signals I-12 and I-15,
respectively. Such signals can also be sent en bloc . After recep-
tion of Signal I-15, the digits of the called subscriber number
continue to be sent so far as they are dialled and available for
sending (overlap method).
The scheme corresponding to that kind of call is identical
with that shown in Figure 4, however, without the signals
corresponding to the calling subscriber number (ID Nj).
Note - As for international calls, the sending sequence
begins with the international prefix, which is followed by the suf-
ficient number of digits of the international number of the called
subscriber to route the call. The remaining sequence is also simi-
lar to that used for national calls in Items a) and b) above.
When configuration presented in S 3.3.4 b) (Signalling Trans-
lation Equipment separated from the Switching Exchanges) is
adopted, signals may be sent forward as soon as they are received
by the Signalling Translation Equipment at the Signalling Transla-
tion Point, although the relative position for sending the calling
subscriber identification (between two determined digits of called
subscriber number) may be at any fixed point.
If the procedures for sending forward signals are defined for
each different type of call, a check towards reception of forward
signals may be made by the Signalling Equipment at the destination
end of the satellite link by simply counting the signals received.
Signals I-12 and I-15 serve as reference points.
3.3.5.3 Relative to the sending of Group B backward signals
A Group B backward signal may be sent at any time during the
period for sending of Group I and II forward signals provided that
there is a condition which must require interruption of the call
setting-up process, such as time-out or congestion at any point of
the national or international network and non-existent national or
international code or non-existent exchange prefix.
3.3.6 Operational procedures of the system
3.3.6.1 Introduction
The Non-Compelled Signalling, based on the Signalling
System R2, is conceived for the purpose of making possible reten-
tion of the mode of operation, facilities and other characteristics
of a national network, which uses the Signalling System R2, after
introduction of telephone satellite communications on a large
scale. Modifications necessary for operation on satellite links
must be restricted only to equipment connected with the involved
links so as to avoid any undesirable effect on the remaining sys-
tem.
The use of the Non-Compelled Signalling requires modifications
only in the equipment connected with satellite links [S 3.3.4 a)].
Besides, a solution which will not interfere at all in the existing
equipment may be also adopted [S 3.3.4 b)].
3.3.6.2 Interface procedures at the signalling translation
points
Figure 5 shows the most general case concerning setting-up of
a call via satellite by means of the Non-Compelled Signalling in a
national network which operates with the Signalling System R2 and
using configuration of S 3.3.4 a).
The signalling equipment which precedes the Signalling
Translation Point at the outgoing end of the satellite link will
operate with the end-to-end method up to this point, at which the
Fully-Compelled Signalling will be converted into the Non-Compelled
Signalling.
The inverse conversion, that is, from the Non-Compelled Sig-
nalling to the Fully-Compelled Signalling, will be performed at the
Signalling Translation Point at the incoming end of the satellite
link, from which signalling will become fully-Compelled using the
end-to-end method.
The procedures carried out towards call setting-up by using
the Non-Compelled Signalling are basically the following for
national calls:
The Signalling Translation Point at the outgoing end of the
satellite link receives the sufficient number of digits to route
the call (ON1 . . . Ni) and then starts (starting point) the pro-
cedures for sending those digits forward in the form of pulses (it
sends the Seizure signal and receives the Proceed-to-Send signal)
and it sends digits from 0 to Ni. The sending sequence continues
through the sending of Signal I-12, which determines the beginning
of transmission of the category (CAT) and number (ID Nj) of the
calling subscriber. Signal I-15 follows after the sending of the
last digit of that subscriber number. Then, the sending of the
digits of the called subscriber number (. . . NK . . .) succeeds up
to the last digit (NL).
The Signalling Translation Point at the outgoing end of the
satellite link starts call routing immediately after receiving the
sufficient number of digits, thus establishing a process of signal-
ling with subsequent signalling equipment in the end-to-end method
up to reception
of Signal A-3 and an End-of-Selection signal (Group B Sig-
nal). At that moment, that last signal is repeated backward in the
form of pulse up to the Signalling Translation Point at the outgo-
ing end of the satellite link. The final signal interchange is car-
ried out between that point and the preceding signalling equipment
(A-3, CAT, B) and then the speech path is set up.
If there is no need to send the calling subscriber number,
only the category is sent forward and Signals I-12 and I-15 are
maintainted before and after the sending of that calling subscriber
category, which is used by the Signalling Translation Point at the
destination end in acknowledgement to Signal A-3 at the end of the
call setting-up procedure.
The signalling process may be interrupted at any time by a
Group B signal, as explained in S 3.3.5.3.
Note - As for international calls, procedures include receiv-
ing of international prefix and international code, but they are
similar to those used for national calls.
If configuration presented in S 3.3.4 b) (Signalling
Translation Equipment separated from the Switching Exchanges) is
adopted, signals in both outgoing and incoming Signalling Transla-
tion Equipment at the Signalling Translation Points may be sent
forward as soon as they are received by Signalling Translation
Equipment.
3.3.7 Multifrequency signalling equipment
Recommendations for Signalling System R2 other than for
exclusive use in Fully-Compelled Signalling are applicable to
Non-Compelled Signalling. Thus, the requirements related to
transmission and to the sending and receiving parts of the mul-
tifrequency equipment may be applied to that signalling. The same
signal senders and receivers specified for Signalling System R2 may
be used.
The use of such signal senders and receivers avoids the
development of new equipment, and they will operate easily in rela-
tion to their sending and receiving characteristics, taking into
consideration that they have been dimensioned for end-to-end opera-
tion, but with Non-Compelled Signalling they operate link-by-link.
3.3.8 Time requirements
3.3.8.1 General
As Non-Compelled Signalling is performed to operate between
two signalling points inserted in a multi-point signalling network
using Signalling System R2, time requirements should be compatible
with the specifications for this system.
3.3.8.2 Time-out conditions
a) In the signalling equipment at the outgoing end
of the satellite link, the time-out delay between the Seizing sig-
nal and the sending of the first forward interregister signal and
between the sending of each two subsequent forward interregister
signals until the reception of the Group B signal should not be
less than 24 s.
b) In the signalling equipment at the incoming end
of the satellite link, the time-out delay between the sending of
the Proceed-to-Send signal and the reception of the first forward
interregister signal and between the reception of each two subse-
quent forward interregister signals until the sending of the
Group B signal should not be less than 24 s.
4 Pulsed line signalling
4.1 Introduction
The line signalling herein presented and foreseen to be used
in FDM carrier circuits is a pulsed, high level, out-of-band sig-
nalling which operates link-by-link. It may also be used on PCM
systems (with channel-associated signalling).
4.2 Description of the signals
4.2.1 Seizure Signal - It is a signal which is sent forward,
from the outgoing junctor, in order to drive the associate incoming
junctor to the seizure condition.
4.2.2 Proceed-to-Send Signal - It is a signal which is sent
backward, from the incoming junctor to the associate outgoing junc-
tor, in order to indicate that a destination interregister signal-
ling equipment has been already seized and that interregister sig-
nalling may start.
4.2.3 Answer Signal - It is a signal which is sent backward,
from the incoming junctor to the associate outgoing junctor, so as
to indicate that the called subscriber has answered.
4.2.4 Clear Back Signal - It is a signal which is sent back-
ward, from the incoming junctor to the associate outgoing junctor,
so as to indicate that the called subscriber has hung up or that a
similar operation has occurred.
4.2.5 Clear Forward Signal - It is a signal which is sent
forward, from the outgoing junctor to the associate incoming junc-
tor, in order to release the equipment involved in the connection.
4.2.6 Release Guard Signal - It is a signal which is sent
backward, from the incoming junctor to the associate outgoing junc-
tor, in response to a Clear Forward signal, so as to indicate that
the release of equipment associated to the incoming junctor has
occurred.
4.2.7 Forced Release Signal - It is a signal which substi-
tutes, after time-out, the Clear Back signal at a charging point.
With reception of Forced Release signal, the speech path is immedi-
ately opened.
4.2.8 Multimetering Signal - It is a signal which is sent
backward, from the incoming junctor to the associate outgoing junc-
tor, according to the cadence corresponding to the charging rate,
as from the multimetering charging point.
4.2.9 Call-Back Signal - It is a signal which is sent for-
ward, from the outgoing junctor to the associate incoming junctor,
when an operator wants to call back the called subscriber (or
another operator) after he has hung up.
4.2.10 Blocking Signal - It is a signal which is sent back-
ward, from the incoming junctor to the associate outgoing junctor,
by means of a manual or automatic procedure, in order to indicate
that the circuit or a group of circuits is blocked.
Taking into consideration the transmission level, the duration
of the signal and the conventional load in satellite circuits, its
use must be avoided when the number of telephone circuits is large
in relation to the total number of circuits of the route. In this
case, when there is blocking, the line signalling system itself
already foresees procedures that can prevent successive losses of
calls, as described in S 4.6.1.
4.3 Characteristics of the signals
4.3.1 Duration of the signals
Line signals show the following durations:
H.T. [B/T1]
TABLE 1
Pulsed Line Signals
Sending Times and Tolerances
_______________________________________________________________________
{
Sending tolerances (ms)
Signal
Forward Backward
_______________________________________________________________________
Seizure 150 _ 30
Proceed-to-send 150 _ 30
Answer or re-answer 150 _ 30
Multimetering 150 _ 30
Call-back 150 _ 30
Clear-forward 600 _120
Clear-back 600 _120
Release guard 600 _120
Forced release 600 _120
Blocking continuous {
-
a)
Short signal:
150 ms
Long signal:
600 ms
}
_______________________________________________________________________
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Table [B/T1], p.
4.3.2 Recognition times of the signals
Recognition times of the signals are presented in Table 2 and
they take into account time distortions introduced by transmission
equipment and tolerances of switching equipment which adopts the
conventional electromechanical technology.
H.T. [B/T2]
TABLE 2
Pulsed Line Signals
Recognition Times and Tolerances
_____________________________________________________________________
Signal Nominal recognition time (ms) Receiving tolerances (ms)
_____________________________________________________________________
Short 80 _ 20
Long 375 _ 75
_____________________________________________________________________
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Table [B/T2], p.
a) The recognition time of short signals ranges
from 80 _ 20 ms to 375 _ 75 ms. Any received signal with duration
between 100 ms and 300 ms will be necessarily recognized as a short
signal.
b) The recognition time of long signals corresponds
to 375 _ 75 ms. Any received signal with duration superior to
450 ms will be necessarily recognized as a long signal.
c) The received signals with duration between
300 ms and 450 ms may be recognized as long or short signals,
depending on the adjustment characteristics of the equipment.
d) The receiver ignores interruptions up to 20 ms.
4.3.3 Minimum interval between signals
The minimum interval between two consecutive signals must be
240 ms at the transmission end. Distortion may reduce this interval
at the receiving end.
4.3.4 Transmission of signals
The transmission of signals between the switching equipment
and the transmission equipment and vice versa is made by sending a
polarity which corresponds to the battery voltage.
4.4 Transmission characteristics of the line signalling in
FDM equipment
4.4.1 Signal sender
The signalling frequency measured at the sending point has a
value of 3825 _ 4 Hz.
The send level of the signalling frequency measured at the
group distribution frame or an equivalent point must be
-5 _ 1 dBm0.
4.4.2 Signal receiver
The receiver must recognize as valid signals which lie between
3825 _ 6 Hz.
The receiving levels are determined in accordance with the
relative levels of the transmission plans adopted by each Adminis-
tration.
4.5 Operational procedure of the system
4.5.1 When the circuit is idle, there is no signal on the
line. The seizure of the outgoing junctor causes the forward send-
ing of a short signal (Seizure signal). This signal causes the
seizure of the associate incoming junctor and the seizure of equip-
ment capable of receiving interregister signals.
4.5.2 Immediately after the seizure of equipment for interre-
gister signalling interchange, the incoming junctor sends back a
short signal (Proceed-to-Send signal).
4.5.3 When called subscriber answers, a short signal (Answer
signal) is sent back, thus causing the start of call charging.
4.5.4 When calling subscriber hangs up, a long signal (Clear
Forward signal) is sent forward, thus causing equipment release.
After such release, a Release Guard signal is sent back and the
circuit comes back to idle condition.
4.5.5 If the called subscriber hangs up first, a Clear Back
signal will be sent and then, after time-out at a determined point
of the network, there will be the sending of a Clear Forward sig-
nal, thus completing the process, as described in S 4.5.4. If
another Answer signal appears during the time supervision period,
timing will be interrupted and the equipment involved will return
to the speech condition. If the calling subscriber hangs up during
the time supervision period, the same procedure as that described
in S 4.5.4 will occur.
After time-out, the Clear Back signal is replaced by the
Forced Release signal between the charging point and the preceding
exchange.
Note - When there is coincidence of two signals, the forward
signal will always prevail.
4.6 Behaviour of the system during interruption in
transmission
4.6.1 Interruption during the Seizure signal
The Seizure signal does not get to the incoming junctor and
therefore there is not its seizure. After time-out, the outgoing
junctor sends the Clear Forward signal. As the incoming junctor has
not been seized, the Release Guard signal will not be sent. So,
time-out in the outgoing junctor occurs and then a maintenance
alarm is activated and another Seizure signal is sent, being fol-
lowed by the Clear Forward signal. Such sequence is repeated at
intervals identical with those of the time supervision period of
the junctor. After the reset up of the transmission system and the
next reception in sequence of the Seizure and Clear Forward sig-
nals, the incoming junctor sends the Release Guard signal, thus
releasing the outgoing junctor.
4.6.2 Interruption during the Proceed-to-Send signal
The Proceed-to-Send signal does not get to the outgoing junc-
tor and therefore interregister signalling does not start. Two
cases are possible:
a) After time-out in the signalling equipment at
the incoming end of the link, the specific interregister backward
signal is sent back. The signalling equipment at the incoming end
of the link releases and the outgoing junctor sends forward the
Clear Forward signal.
b) After time-out, the signalling equipment at the
outgoing end of the link releases and the outgoing junctor sends
forward the Clear Forward signal.
4.6.3 Interruption during the Answer signal
The Answer signal does not get to the outgoing junctor and the
call may be completed even if charging has not started. After
time-out in the origin, the Clear Forward signal is sent. The
incoming junctor sends the Release Guard signal, thus releasing the
outgoing junctor.
4.6.4 Interruption during the Clear Forward signal
The Clear Forward signal does not get to the incoming junctor
and therefore it cannot send the Release Guard signal. After
time-out, a maintenance alarm is activated and the Seizure signal
is sent, being followed by the Clear Forward signal. Such sequence
is repeated at intervals identical with those of the time supervi-
sion period of the outgoing junctor until the Release Guard signal
is received.
If there is a short interruption in the transmission system,
thus preventing reception of the Clear Forward signal at the incom-
ing junctor and in case the called subscriber will hang up during
the time supervision period of the outgoing junctor, the Clear Back
signal will be taken as a Release Guard signal and therefore there
will be the release in the origin. However, the equipment which has
not received the Clear Foward signal will remain set up until it
has been requested again and released by another call, which will
not be successful.
4.6.5 Interruption during the Clear Back signal
The Clear Back signal does not get to the outgoing junctor and
the release of the equipment will be dependent on the calling sub-
scriber hang-up.
4.6.6 Interruption during the Release Guard signal
The Release Guard signal does not get to the outgoing junctor
and, after time-out, the procedure used is the same as that esta-
blished in S 4.6.4.
4.6.7 Interruption during the Forced Release signal
The Forced Release signal does not get to the outgoing junctor
and the release of the equipment will be dependent on the calling
subscriber hang-up.
Figure 1, p.20
Figure 2, p.21
Figure 3, p.22
Figure 4, p.23
Figure 5, p.24